1. Field of the Invention
The present invention relates to a carbon monoxide reduction catalyst for smoking articles and a method for producing the same.
2. Description of the Related Art
It has been proposed that, in order to remove carbon monoxide present in cigarette mainstream smoke, a noble metal catalyst or a transition metal oxide catalyst is added to shredded tobacco, a cigarette paper or a filter. These catalysts promote a reaction that carbon monoxide is oxidized and converted into carbon dioxide. For example, Patent Literature 1 discloses that nano-scale metal particles or nano-scale metal oxide particles are carried on carrier particles having a high surface area and are added in shredded tobacco and the like in order to convert carbon monoxide into carbon dioxide. Further, Patent Literature 2 describes that a partially reducing additive in the form of nano-particles is added as a carbon monoxide reduction agent to a cut tobacco filler. Patent Literature 3 describes that nano-particles of, for example, a metal oxide are physically deposited on, for example, a tobacco cut filler, as an oxidizer that converts carbon monoxide into carbon dioxide. As mentioned above, these three Patent Literatures disclose the use of nano-particles of a metal oxide. However, nano-particles are not easily handled when they are applied to smoking articles, giving rise to the complexity of a process of producing smoking articles. Further, in Patent Literature 1, a nano-catalyst is supported by a carrier and therefore, the production cost tends to increase because the carrier is used. Patent Literature 4 discloses that when a carbonaceous heat source used in smoking articles is produced, a carbonaceous heat source material is treated with a sol containing a metal oxide precursor to be converted into a metal oxide catalyst that converts carbon monoxide into a harmless material.